Nitrogen Activation via Three-Coordinate Molybdenum Complexes: Comparison of Density Functional Theory Performance with Wave Function Based Methods

Abstract

Obtaining an accurate theoretical model for the activation of dinitrogen by three-coordinate molybdenum amide complexes (e.g. Mo(NH2)3) is difficult due to the interaction of various high- and low-spin open-shell complexes along the reaction coordinate which must be treated with comparable levels of accuracy in order to obtain reasonable potential energy surfaces. Density functional theory with present-day functionals is a popular choice in this situation; however, the dinitrogen activation reaction energetics vary substantially with the choice of functional. An assessment of the reaction using specialized wave function based methods indicates that although current density functionals in general agree qualitatively on the mechanistic details of the reaction, a variety of high-level electron correlation methods (including CCSD(T), OD(T), CCSD(2), KS-CCSD(T), and spin-flip CCSD) provide a consistent but slightly different representation of the system.

The influence of peripheral ligand bulk on nitrogen activation by three‐coordinate molybdenum complexes—A theoretical study using the ONIOM method

“…Our recent theoretical study 13 on the Mo(NH 2 ) 3 model system highlighted the variation between different DFT methods. As a result of this, here, we have performed single-point calculations on our ONIOM optimized geometries using both density functional and wave function-based methods.…”

“…Info.). Conformer searching was carried out on all structures and given that the central atoms form a rigid and well studied 13,14,18,25,28,29 basis for the molecule, conformational searching centered around peripheral ligand rotation. Frequency calculations were performed, with structures characterized as minima or transition states based on the observed number of imaginary frequencies.…”

“…This initial reaction profile as proposed by Morokuma's group 12 has been further refined by including the important spin crossings that occur throughout the reaction. Stranger and Yates 13,14 produced a detailed outline that involved an initial dinitrogen encounter with the quartet reactant, followed by spin flip to the doublet encounter complex where the dinitrogen is bound end-on to the Mo metal center with a rotated amide providing additional electron density and stability to the structure. The doublet encounter complex then interacts with another reactant forming a linear L 3 MoNNMoL 3 triplet intermediate, without barrier.…”

Multiple Reaction Pathways in Rhodium‐Catalyzed Hydrosilylations of Ketones

“…For general accuracy of the energetics in organometallic reactions, benchmark calculations have shown this level of theory to yield satisfactory results. [35,[36][37][38][39][40][41][42][43][44][45] Stationary points on the potential-energy surface were characterized as either minima or transition states by the presence of (respectively) zero or one significant imaginary frequency in the BP86/SV(P) vibrational spectrum, obtained by second analytic derivative calculations. [46,47] All Gibbs free-energy values refer to 298.15 K and 0.1 MPa pressure.…”

Nitrogen Fixation under Mild Ambient Conditions: Part I—The Initial Dissociation/Association Step at Molybdenum Triamidoamine Complexes

“…Furthermore, all DFT studies on FeMoco rely on pure density functionals like (R)PBE [23,24] and BP86, [25,26] while it is well known that the energetical ordering of different spin states can hardly be reproduced without inclusion of exact exchange in critical cases. [27][28][29][30][31][32][33][34][35][36] Very recently Graham et al [37] presented a sophisticated comparison of DFT and coupled cluster results for nitrogen activation at a three-coordinate molybdenum metal fragment yielding tetrahedral dinuclear dinitrogen complexes. They found B3LYP energies in agreement with CCSD(T) results, while other density functionals yield substantially different results.…”